There is only one file type that uses the .MB extension:
Maya Binary Project File
Project file created with Maya, a 3D modeling and animation program; contains three-dimensional models, textures, lighting properties, and animation data; saved in a binary format instead of the ASCII text format used by Maya .MA files.
Maya was originally developed by Alias Wavefront. The company was acquired by Autodesk in 2006.
Updated: December 11, 2014